1. Field of the Invention
The present invention concerns single-pole and multipole electrical circuit breakers in which maximum contact opening is achieve in a circuit breaker of minimum size. The present invention includes means affording maximum accuracy in control of the switching means, as well as improved safety.
2. Discussion of the Related Art
Commonly assigned U.S. Pat. Nos. 3,959,755 to Harper et al and 4,117,285 to Harper disclose representative conventional circuit breakers, comprising a stationary electrical contact, a movable electrical contact mounted on a movable contact arm, means for manually opening and closing the contacts, and means for automatically opening the contacts in response to an overcurrent through the breaker. The component parts of the breaker are enclosed in an insulating plastic housing.
Commercial circuit breaker manufacturers generally manufacture a complete product line composed of a number of breaker sizes, each one covering a different (although sometimes overlapping) operating current range. To date, each breaker size has required its own component and case sizes. In general, each component and case size combination is useful in circuits having only a single current rating range. The need to have a different set of component and case sizes for each current rating has added to the overall cost of breakers of this general type. Heretofore, a variety of factors has dictated breaker sizes.
One such factor relates to the minimum gap requirement between contacts that must be met for a given current rating, when the breaker contacts are manually opened, as well as when they are tripped open automatically. (Many breakers separate their contacts a first distance when manually opened and a distance when automatically tripped.) It is necessary to make the breaker sufficiently large so that the minimum gap requirement is met in the manual and automatic modes, whichever results in a smaller gap. This requirement has an effect on the overall size of the breaker.
As the current carrying capacity (or rating) of the breaker increases, the gap between the electrical contacts of the breaker in the OFF (or open) position must increase proportionately. Since known circuit breakers are generally capable of separating their electrical contacts only a relatively limited distance compared to the overall size of the breaker, it has been necessary to manufacture increasingly larger circuit breakers in order to obtain the greater spacing between electrical contacts in the OFF position required for higher current ratings.
The overall dimensions of circuit breakers are also determined in part by the need to satisfy industry safety standards. Industry standards, such as the German VDE and the proposed IEC standard, for example, typically require that the plastic casing of the breaker be designed to prevent access by external objects, such as a human finger, to within a given distance of electrically conductive parts of the breaker. When breakers are employed in a multipole arrangement, it is also required that a specified distance be maintained between conductive parts of adjacent breaker poles.
Multipole circuit breakers typically comprise several interconnected single-pole units positioned adjacent each other. The manual switching handles of the respective breakers may be connected to each other for simultaneous manual actuation of all poles. Alternatively, or in addition to connecting the respective manual switching handles, means may be provided to trip open automatically all of the breaker poles simultaneously when any one of them is tripped.
Conventional multipole circuit breaker arrangements include a trip lever mechanism associated with each pole of the multipole circuit breaker. Each trip lever includes a portion for joining it to adjacent trip levers. If any pole is tripped open by an overcurrent, the breaker mechanism of that pole causes the trip lever to pivot about its mounting axis. The pivotal motion of one lever causes all the interconnected trip levers to similarly pivot. Each lever may include an arm for striking the armature or toggle mechanism of its respective pole, and causing each pole to be tripped open.
This apparatus, while generally satisfactory, suffers from certain drawbacks. Upon automatic tripping of a first pole, a rather lengthy series of mechanical movements must take place in order to trip each breaker pole. The tripped pole must impart pivotal movement to its associated trip lever; that trip lever must impart similar motion to the other trip levers to which it is joined. Each trip lever must contact the armature of its associated pole; and the armatures must trip open each respective pole. In known breakers, a pin and socket or similar arrangement is used for joining several trip levers to each other. Due to manufacturing tolerances, the fit between levers is likely to be somewhat loose, and the motion of some levers will generally lag behind that of other levers by as much as several thousandths of an inch. The effect of such mechanical delays multiplies as the number of poles increases. These mechanical delays cause temporal delays in breaker tripping; ultimately this can result in damage to the circuit intended to be protected. Ideally, therefore, tripping of all poles should occur virtually simultaneously upon tripping of any one pole.
In another known arrangement, a rotatable trip bar extends through each pole of the multipole breaker. When a pole is tripped, the bar rotates to trip open the remaining poles. While this device does not suffer from backlash delays caused by the above-described loose-fitting pin joining means, it is still necessary for the device to execute a lengthy sequence of mechanical movements in order to trip open all of the breakers. The first tripped breaker must strike its associated trip lever; the trip lever must strike a tab of the rotatable trip bar. The remaining tabs of the trip bar must contact the armatures of the remaining breakers; and the armatures must strike the automatic tripping means of each breaker.
Additionally, it is conventional practice to join the manual switching handles of a multipole circuit breaker by inserting a pin through a hole in each of the several handles. Manufacturing tolerances result in a somewhat loose fit of the pin within each handle. Some of the handles will therefore lag behind others when all are moved together to open or close all of the poles. Consequently, the electrical contacts of the several poles will not open or close at precisely the same time.
An additional drawback of the manual switching means associated with many known circuit breakers is the relatively long motion required to move the switching handle between the ON and OFF positions. As the length of the handle "throw" increases, the time required to manually open the breaker also increases. Although measured in small fractions of a second, such time differences are significant when rapid interruption of an electrical circuit is necessary. This problem is compounded by the backlash and delay resulting from the loose fitting pin typically joining the handles of a multipole circuit breaker. A desirable reduction in the "throw" between the ON and OFF positions of the handle is generally accompanied by an undesirable reduction in the maximum separation between electrical contacts of the circuit breaker in the OFF position.
The present invention is directed, in part, to overcoming the above-mentioned problems associated with known circuit breakers.